The trial of the doctor charged in Michael Jackson's death resumed Wednesday after days of delay, with jurors hearing from a leading expert on the powerful anesthetic propofol that authorities say killed the King of Pop.

Dr. Steven Shafer's early testimony focused on his lengthy credentials, studies he has helped create, and his work crafting guidelines and warnings that are included with every bottle of propofol.

Prosecutors claim Dr. Conrad Murray ignored those warnings by giving Jackson the anesthetic in the bedroom of his rented mansion.

Shafer is expected to introduce a video demonstration that shows the proper procedures for administering propofol in a hospital setting, where the drug is supposed to be used.

Superior Court Judge Michael Pastor ruled that portions of the video, which depicts the setup of an operating room and what medical personnel are supposed to do if a patient's heart stops, could be shown to jurors.

Before the video was played, Shafer told jurors he is not charging for his work on the Jackson case, in part because he wants to restore public confidence in the medication and doctors.

"I am asked every day in the operating room, 'Are you going to give me the drug that killed Michael Jackson,'" Shafer said. "This is a fear that patients do not need to have."

Shafer, who is a researcher and a practicing anesthesiologist, is the prosecution's final witness in its case against Murray, who has pleaded not guilty to involuntary manslaughter. He used a bottle of propofol he brought to court to demonstrate how a syringe can be used to obtain the drug from its glass vial.

Pastor canceled testimony Tuesday to give defense attorneys time to research new test results conducted by coroner's officials on the level of the sedative lorazepam in Jackson's body.

Murray's attorneys have claimed lorazepam levels in the singer's stomach contents suggested he may have taken several pills without his doctor's knowledge in the hours before his death.

Murray has acknowledged giving Jackson doses of propofol in the pop superstar's bedroom as a sleep aid. However, his attorneys have said that the amount of propofol given to Jackson on the day he died was too small to cause his sudden death at age 50.

Deputy District Attorney David Walgren gas said the new results from the coroner's office show that levels of lorazepam in Jackson's body were lower than the defense claimed and were inconsistent with the theory that Murray's attorneys had presented to jurors.

Lead defense attorney Ed Chernoff said he was seeking additional testing from an independent lab to confirm or disprove the coroner's results, but it would take several days for the defense to get the answers it needs.

Walgren agreed that he would not raise the issue of the new tests until after the defense team presents its case.

Chernoff complained about the video on propofol procedures that will be shown to jurors. "This is a dramatization," he said. "The information can be described."

The video simulates an operating room environment and includes segments in which various medical and life-saving equipment present in the room are described in detail.

"This is designed to assist the jury to better understand the testimony of Dr. Shafer," Walgren said.

Pastor said the video was highly relevant, but asked prosecutors to edit out certain portions before playing it in court.

Murray's attorneys will begin calling witnesses Friday. They plan to call 15 witnesses, including police detectives, character witnesses and Randy Phillips, the head of AEG Live, the promoter of Jackson's planned series of comeback concerts.

Chernoff said many of the witnesses will be brief and the defense should rest its case by Wednesday.

Murray's attorneys are also going to call one of Shafer's colleagues, Dr. Paul White, as an expert to try to counter the prosecution's case.

Prosecution witnesses have repeatedly faulted Murray for his care of Jackson, noting that his use of propofol as a sleep aid was outside the drug's intended use. They have also faulted Murray for not calling 911 sooner, for botching resuscitation efforts and for lying to paramedics and emergency room doctors about the drugs he had given Jackson.